迈丹断裂阿合奇段晚第四纪活动特征与地震危险性分析
发布时间：2018-08-28 09:52
【摘要】：迈丹断裂是柯坪逆冲推覆构造的根部断裂,根据仪器记录,它的地震活动相对较弱,因此多数学者认为该断裂晚第四纪以来活动性不强,而野外考察发现阿合奇段晚第四纪以来多次活动,其活动频率甚至超过了推覆体前锋的逆冲断裂,因此迈丹断裂并不完全遵循北天山前展式构造模式,是一条反序型活动逆冲断裂。笔者根据前人资料并在卫星影像遥感解译和野外地质调查的基础上,确定了阿合奇段的几何形态和空间展布特征。开展野外地质调查,厘清水系、山脊、冲洪积扇的分布特点,并寻找断裂最新活动的证据,如断层陡坎,河流阶地冲洪积扇及山脊位错等地貌现象。系统测量、对比分析断层陡坎高度、发育程度、走向、错断地貌面时代。对断裂带的空间展布特征进行追踪并对断裂带地质地貌特征展开详细调查,收集分析相关资料,对断裂晚第四纪活动性做出判断并对断裂带进行分段研究。选取合适位置开挖探槽、对探槽内地震事件进行分析,采集年龄样品并利用获得的活动构造定量测量参数对断裂的危险性进行初步评估。获得的主要结论有:(1)迈丹断裂是柯坪逆冲推覆构造系统的北边边界断裂,是西南天山对冲挤压边界构造变形带与塔里木盆地的一部分。由3条断裂彼此近于平行,总体走向北东东,倾向向北的断裂组成,形成叠瓦状构造,向深部延伸,共同组成逆冲推覆构造系统。迈丹断裂形成于一个长期的递进变形过程当中,最新形成的F1阿合奇段具有最新的活动性。(2)迈丹断裂可能表现为另外一种意义上的无序性。迈丹断裂带有长期的发育历史,存在多排平行的地表断层陡坎,断裂数目和分支多,地震破裂的路径具有很强的随机性,甚至也有可能存在多条断裂同时发生同震破裂的地震事件。(3)阿合奇段晚第四纪仍在强烈活动。阿合奇段长约60km,由2-4条产状相近且大致平行的次级逆断层组成,倾向向北,倾角相近(20-70°),组成一组铲式逆冲断层,并伴生有一条反倾的逆断裂。阿合奇段的地层发育受主逆断裂控制,下盘地层基本没有变形,地层的变形主要发生在上盘。沿主断裂普遍伴生反冲逆断裂,它属于浅部破裂,其破裂面深度有限,主断裂和反向断裂之间部分被挤出。从野外调查情况来看,反冲断裂的规模远远小于主逆断裂,反冲断裂受主逆断裂控制与主逆断裂的同期发育,但不具备发震能力。(4)阿合奇段存在多处冲沟水系和阶地边缘被左旋错动的痕迹。阿合奇西北洪积扇上的冲沟普遍发生左旋位错,去除非构造因素,左旋走滑距离普遍为陡坎高度的1.5-3倍。因阶地面年龄由于测年周期原因还没能得到,对其走滑速率还不能做出估计。(5)阿合奇段主要表现为山前洪积扇的断错变形,通过实测计算,认为其单次破裂导致的地表垂直错距为2.9m,垂直滑移速率约为0.67-0.75 mm/a,由断层活动造成的地壳水平缩短速率为1.15mm/a。玉山古溪古地震探槽揭示了其古地震离逝时间为1.76±0.22 ka。(6)地震危险性分析。首先依据地震空区理论,定性地得出了迈丹断裂处于一个带状地震空区之内,根据该地震空区的表现形式可知,该地震空区应属于Mogi所定义的第二类地震空区。然后基于震级与平均同震位错量之间的统计关系式最终得到阿合奇段潜在最大震级为7.5级,并利用垂直滑动速率和探槽中获取的地震离逝时间得到阿合奇段积累的地震矩能量值,进一步得到阿合奇段潜在震级为7.4级;根据地震原地复发的时间可预报模式,利用滑动速率和同震位错等定量参数得出地震复发间隔约为3626-3870a;最后根据建立于概率论和地震原地复发理论基础上的概率评估方法最终得到未来50a、100a、200a三个时间段所积累的条件概率。
[Abstract]:Maidan fault is the root fault of the Keping thrust nappe structure. According to the instrumental records, its seismic activity is relatively weak, so most scholars think that the activity of the fault is not strong since the late Quaternary. Field investigation shows that the Aheqi section has been active many times since the late Quaternary, and its activity frequency even exceeds the thrust fault of the nappe front. Therefore, the Meidan fault does not completely follow the North Tianshan Piedmont structural model and is an anti-sequence active thrust fault. Based on the data of predecessors and on the basis of remote sensing interpretation of satellite images and field geological survey, the geometry and spatial distribution characteristics of the Aheqi section are determined. Distribution characteristics of alluvial fans and evidence of the latest activities of faults, such as fault scarps, alluvial fans on river terraces and mountain ridge dislocations, etc. Systematic measurement, comparative analysis of the height of fault scarps, development degree, strike, staggered geomorphological age. Tracking the spatial distribution characteristics of fault zones and geological and geomorphological characteristics of fault zones. Detailed investigation was carried out, relevant data were collected and analyzed, the Late Quaternary activity of the fault was judged, and the fault zone was studied in segments. The main conclusions are as follows: (1) Maidan fault is the northern boundary fault of Keping thrust nappe structure system, which is a part of the southwest Tianshan thrust compression boundary structural deformation belt and Tarim Basin. Madan fault is formed in a long-term progressive deformation process, and the newly formed F1 Aheqi section has the latest activity. (2) Madan fault may show another sense of disorder. (3) The Aheqi section is still active in the late Quaternary. The Aheqi section is about 60 km long and consists of 2-4 secondary reverse faults with similar occurrence and approximately parallel occurrence. It is inclined to the north with similar dip angle (20-70). A group of shovel thrust faults are formed and accompanied by an inverted fault. The strata of Aheqi section are controlled by the main inverted fault. The lower wall strata have no deformation basically. The deformation of strata mainly occurs in the upper wall. According to the field investigation, the scale of the thrust fault is much smaller than that of the main thrust fault. The thrust fault is controlled by the main reverse fault and develops simultaneously with the main reverse fault, but it does not have the seismogenic ability. (4) There are many left-handed dislocations of gully drainage system and terrace margin in Aheqi section. Left-lateral strike-slip distances are generally 1.5-3 times of the height of the steep ridge, and the rate of strike-slip can not be estimated because the terrace age is not yet available due to the dating period. (5) The Aheqi section is mainly characterized by the fault-slip deformation of the piedmont alluvial fan. The vertical offset of the surface caused by rupture is 2.9 m, and the vertical slip rate is about 0.67-0.75 mm/a. The horizontal crustal shortening rate caused by fault activity is 1.15 mm/a. The Guxi paleoseismic trench in Yushan reveals that the paleoearthquake departure time is 1.76.22 ka. (6) Seismic hazard analysis. Firstly, according to the theory of seismic empty area, Maidan is qualitatively obtained. The fault is located in a zonal seismic gap. According to the manifestation of the seismic gap, the seismic gap should belong to the second type of seismic gap defined by Mogi. Then, based on the statistical relationship between magnitude and mean coseismic dislocation, the potential maximum magnitude of Aheqi section is 7.5, and the vertical slip rate and exploration are used. The seismic moment energy accumulated in Aheqi section is obtained from the time of seismic departure obtained in the trough, and the potential magnitude of Aheqi section is 7.4. According to the time-predictable model of earthquake recurrence in situ, the recurrence interval is about 3626-3870a by using quantitative parameters such as slip rate and seismic dislocation. The conditional probability accumulated in the next 50, 100 and 200 years can be obtained by the probability evaluation method based on the theory of in situ earthquake recurrence.
【学位授予单位】：中国地震局兰州地震研究所
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P315.2
本文编号：2209036
[Abstract]:Maidan fault is the root fault of the Keping thrust nappe structure. According to the instrumental records, its seismic activity is relatively weak, so most scholars think that the activity of the fault is not strong since the late Quaternary. Field investigation shows that the Aheqi section has been active many times since the late Quaternary, and its activity frequency even exceeds the thrust fault of the nappe front. Therefore, the Meidan fault does not completely follow the North Tianshan Piedmont structural model and is an anti-sequence active thrust fault. Based on the data of predecessors and on the basis of remote sensing interpretation of satellite images and field geological survey, the geometry and spatial distribution characteristics of the Aheqi section are determined. Distribution characteristics of alluvial fans and evidence of the latest activities of faults, such as fault scarps, alluvial fans on river terraces and mountain ridge dislocations, etc. Systematic measurement, comparative analysis of the height of fault scarps, development degree, strike, staggered geomorphological age. Tracking the spatial distribution characteristics of fault zones and geological and geomorphological characteristics of fault zones. Detailed investigation was carried out, relevant data were collected and analyzed, the Late Quaternary activity of the fault was judged, and the fault zone was studied in segments. The main conclusions are as follows: (1) Maidan fault is the northern boundary fault of Keping thrust nappe structure system, which is a part of the southwest Tianshan thrust compression boundary structural deformation belt and Tarim Basin. Madan fault is formed in a long-term progressive deformation process, and the newly formed F1 Aheqi section has the latest activity. (2) Madan fault may show another sense of disorder. (3) The Aheqi section is still active in the late Quaternary. The Aheqi section is about 60 km long and consists of 2-4 secondary reverse faults with similar occurrence and approximately parallel occurrence. It is inclined to the north with similar dip angle (20-70). A group of shovel thrust faults are formed and accompanied by an inverted fault. The strata of Aheqi section are controlled by the main inverted fault. The lower wall strata have no deformation basically. The deformation of strata mainly occurs in the upper wall. According to the field investigation, the scale of the thrust fault is much smaller than that of the main thrust fault. The thrust fault is controlled by the main reverse fault and develops simultaneously with the main reverse fault, but it does not have the seismogenic ability. (4) There are many left-handed dislocations of gully drainage system and terrace margin in Aheqi section. Left-lateral strike-slip distances are generally 1.5-3 times of the height of the steep ridge, and the rate of strike-slip can not be estimated because the terrace age is not yet available due to the dating period. (5) The Aheqi section is mainly characterized by the fault-slip deformation of the piedmont alluvial fan. The vertical offset of the surface caused by rupture is 2.9 m, and the vertical slip rate is about 0.67-0.75 mm/a. The horizontal crustal shortening rate caused by fault activity is 1.15 mm/a. The Guxi paleoseismic trench in Yushan reveals that the paleoearthquake departure time is 1.76.22 ka. (6) Seismic hazard analysis. Firstly, according to the theory of seismic empty area, Maidan is qualitatively obtained. The fault is located in a zonal seismic gap. According to the manifestation of the seismic gap, the seismic gap should belong to the second type of seismic gap defined by Mogi. Then, based on the statistical relationship between magnitude and mean coseismic dislocation, the potential maximum magnitude of Aheqi section is 7.5, and the vertical slip rate and exploration are used. The seismic moment energy accumulated in Aheqi section is obtained from the time of seismic departure obtained in the trough, and the potential magnitude of Aheqi section is 7.4. According to the time-predictable model of earthquake recurrence in situ, the recurrence interval is about 3626-3870a by using quantitative parameters such as slip rate and seismic dislocation. The conditional probability accumulated in the next 50, 100 and 200 years can be obtained by the probability evaluation method based on the theory of in situ earthquake recurrence.
【学位授予单位】：中国地震局兰州地震研究所
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P315.2
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